Black Holes Explained

A lot of interesting things happen around and inside Black holes, which is what makes them so fascinating - Andrew Hamilton

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What Is a Black Hole
What Is a Black Hole

Black Holes: Discovery, Facts and Theories

A Black hole has always been a thing of immense wonder. Even the most fervent scientists have been unable to fully understand a black hole. A part of its magnificence probably lies in the fact that it still has certain mysteries associated with it. The more you find out about black holes, the more mesmerized you become. So, if you are looking to learn about black holes and possess a desire to try and understand them better, then, stick around, this article is just for you.

Content

  1. What are black holes?
  2. Creation of black holes
  3. The death of black holes
  4. What’s inside a black hole?
  5. Types of black holes
  6. Black holes fun facts
  7. Black Hole Infographic

What are black holes?

Black holes are where God divided by zero.--Albert Einstein Click To Tweet

According to Wikipedia “A black hole is a region of spacetime exhibiting gravitational acceleration so strong that nothing—no particles or even electromagnetic radiation such as light—can escape from it“. Most black holes are created when stars implode. The gravity at the centre of the star reaches such high values that the star can no longer sustain the reactions that take place at its core. This implosion gives rise to a body of immensely high gravitational pull, called the black hole. These black holes are said to have an extremely high gravitational pull, which, led to the notion that black holes suck in everything around them. Albert Einstein has been credited for predicting the existence of black holes through his general theory of relativity. However, the term ‘black hole’ was coined by John Wheeler.

Creation of black holes

Cygnus X-1 black hole illustration
Cygnus X-1 (the image is an artist’s impression). Image Source: Sun.org

So, how are black holes formed? So, we all know that there are trillions of stars out there in the universe and all these stars continuously undergo fission reaction to keep shining. But, there comes a point when the star has very little fuel to burn out or the star gets receives extra matter in a way that does not raise its core temperature, in both these cases the star collapses. If the mass of the collapsing star is greater than a threshold then it will form a black hole. These black holes are called stellar black holes. The said threshold is called the Tolman–Oppenheimer–Volkoff limit which is 3-4 solar masses(M)

           M = (1.98847±0.00007)×1030 kg

This is not the only way by which black holes can form. Black holes can also form by high energy collisions which can achieve sufficient density. However, till now we didn’t detect any such events directly or indirectly probably because of mass-imbalance in particle accelerators. Thus, scientists came to the conclusion that there might be some lower boundary of mass for black holes to form and that would lie around Planck mass.

          Planck mass = mP=ħ c/G ≈ 1.2×1019 GeV/c2 ≈ 2.2×10−8 kg

Where,

  • ħ is the Planck’s constant
  • c is the speed of light
  • G is the universal gravitation constant
  • e is the charge of an electron
  • V is 1 volt
  • eV/c2 is commonly used to express mass in particle physics

The outer visible part of the black hole is referred to as the event horizon. In other words, the event horizon is the boundary of the black hole. The innermost part of the black hole is, what scientists call, the singularity. The constituents of a black hole are not quite known to even the most ardent scientists who study black holes.

The death of black holes

Black holes do not last forever either. In an excruciatingly slow process, black holes emanate energy and become hotter and hotter. Black holes, in this process, begin to grow smaller and smaller. They eventually disintegrate in a massive and spectacular manner, with an explosion. This entire process is attributed to the empty space around the black hole. This disintegration is often referred to as black hole evaporation.

You might have heard that the empty space is not actually empty. This is true, empty space consists of virtual particles that randomly come into existence and cancel each other out every now and then. The pair of particles that cancel each other out, is generally referred to as, the particle-antiparticle pair. When this process takes place at the event horizon of the black hole, some particles enter the black hole, while others escape outwards into space.

This results in the loss of energy of the black hole. This loss causes the black hole to become smaller. Initially, this process is slow, but, it soon picks up the pace and becomes faster. This radiation of energy by the black hole is called the Hawking radiation, named after probably one of the most renowned physicists of the recent past, Dr Stephen Hawking.

Star_Life_Cycle_Chart
This flow chart shows the life cycle of stars from birth to remnant stages. Image Source: Wikipedia

What’s inside a black hole?

To be honest, nobody really knows for sure. It is highly unlikely that you would find someone on the face of the earth who could tell you with a great deal of certainty, what exists inside a black hole. The black hole, due to its immense gravitational pull, does tend to pull most entities that are present in its proximity. However, the belief that it attracts particles and bodies towards it, is a misconception. A black hole does not attract entities towards itself, it merely consumes the bodies that are already close to it. That is, if an entity is far away from the black hole, the black hole would not cause the entity to move closer towards the black hole, however, if the entity were in the devouring range of the black hole, it would inadvertently get sucked in.

Nothing is said to escape from the black hole. Even light can’t escape its clutches. To escape from the inside of a black hole, it is said that you would have to be travelling at speeds greater than the speed of light which is not possible according to Einstein’s theories. It is believed that most of the mass of the black hole is concentrated at its centre. This part of the black hole where the mass is said to accumulate is called the singularity.

To figure out what actually is inside a black hole, we would have to send something into it. The problem with this is that anything that enters the black hole cannot return from it. It is highly likely that we will never find out what actually is inside of a black hole.

If you have ever thought to yourself that it would be fascinating to enter a black hole and have ever considered going into one, you should probably reconsider. The larger the black hole, the more intact you are likely to be when you enter, but, there does not exist a black hole that would not kill you as soon as you reach the event horizon. You would get spread, elongated and ripped apart in what is known as spaghettification. Spaghettification is the process in which objects are ripped apart due to the strong gravitational pull of the black hole.

Types of black holes

Blackholes are considered to be of three main types, based on their mass. They are

  1. Stellar black holes
  2. Supermassive black holes
  3. Miniature black holes.

Stellar black holes are those that are formed by the collapsing of the stars. The exact process of formation of stellar black holes is mentioned above The masses of these black holes generally range from 5 to several times the mass of the sun.

Supermassive black holes, on the other hand, have masses that are several hundred or thousands of times the mass of the sun. It is hypothesized that every galaxy in the universe has a supermassive black hole at its centre. Sagittarius A is the black hole considered to be at the centre of the Milky Way. Some scientists also believe that these supermassive black holes have existed since the creation of the universe, or at least, since the creation of each galaxy.

Miniature black holes, as the name suggests, possess the smallest mass of all black holes. There was a time when physicists and astronomers believed that the stellar black hole was the smallest form of black holes. Stephen Hawking introduced the concept that there might exist black holes smaller than the mass of the stellar black hole. These are said to be primordial black holes. Primordial black holes are those that have existed since the Big Bang. These are speculated to have been formed due to the fluctuations in the density of the universe. Theoretically, anything that can have its mass densely condensed and possess an escape velocity greater than the speed of light can become a black hole but experimentally a black hole can possess any mass equal to or greater than the Planck mass.

Planck mass= 2.2×10−8 kg or 22 micrograms

Speaking about its radius, since the escape velocity must be greater than the speed of light, the Schwarzschild radius comes into the picture and it is,

R= 2GM/c^2

Where,

G is the gravitational constantc is the speed of light, and M the mass of the black hole.

Schwarzschild radius is the parameter that corresponds to the radius of the event horizon of the black hole. Every quantity of mass possesses this parameter.

Black holes facts

  • Black holes are said to grow when they consume objects and bodies in space.
  • Black holes have such powerful gravitational pull that not even light can escape it.
  • Black holes are gigantic and are often several times the size of the sun.
  • Black holes are often considered to be perfect black bodies since they do not reflect light.
  • The process of death of black holes is unimaginably slow. It takes a whopping 10^67 to 10^100 years for a black hole to eventually die.
  • There exists a black hole at the centre of the Milky Way. It is called Sagittarius A and is situated at a distance of 26,000 light years from the Solar system.

Even today, there is rigorous research going on to completely understand black holes. Recently there was a major achievement in this research and that was getting the first-ever image of a black hole.


Scientists are now planning to get improved pictures of black holes. Let us hope that uncover the secrets of cosmos and answer some questions which have been daunting scientists from centuries

Neil Armstrong, widely renowned for being the first man to step on the moon, once said, “Mystery creates wonder and wonder is the basis of man’s desire to understand”. Perhaps, there exists no phenomenon in the world that epitomizes the saying more than a black hole does. Black holes are incredibly fascinating and are surrounded with so much mystery that one cannot help but be enamoured by it. However, black holes are quite dangerous, nonetheless. If one were to travel anywhere close to one, they would be sucked into it with no point of return. In all honesty, it would be truly amazing to venture into a black hole to find out what it consists of, but, it most certainly is not worth the risk. A simile that best sums up the situation goes something like

Black holes are like clickbait, you want to go in, but once you do, you regret it Click To Tweet

What do you think about a black hole? Would you like to travel across a black hole and come back if some phenomena allowed it? Tell us with a short and quick comment.

Black Hole Infographic

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Black Hole Infographic

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